The invention relates to a method for the `continuous monitoring of a gas mixture,` in particular a mixture of hydrocarbon and air, by means of flame ionization, for example in painting plants and coating plants, in which at a plurality of spatially separate points of the plant gas samples are continuously withdrawn and are supplied to a flame ionization detector and associated with each withdrawal point is an ionization detector which is controlled by a programmer which is provided with an alarm means which responds on occurrence of a fault.
The use of flame ionization and the use of flame ionization detectors, hereinafter referred to as FIDs, for measuring and investigating gas mixtures is known.
With the FID the total concentration of the hydrocarbons is determined whilst the concentration of the individual components of the gas mixture is determined by means of gas chromatographs.
Gas mixtures, for example in painting plants or coating plants, contain various components which can be highly explosive.
For example, in the electrical industry wires are coated with insulating materials, in the furniture industry chip boards are provided with veneers and in the construction industry structural slabs or beams are coated with plastics; the same applies to the packaging industry in which webs of a support material are laminated with plastic layers.
Common to all these methods is that the coated materials or workpieces are led through drying apparatuses in which the solvents used in the coating must emerge in vapour form in the drying operation and be led off.
As already mentioned, these solvent vapours may be highly explosive and as a rule they are conducted to an afterburning apparatus and there burnt or supplied to a solvent recovery apparatus.
It must be ensured that these solvent vapours do not ignite themselves, which can lead to serious explosions and destruction of the entire plant, and that their concentrations remain adequately far from their so-called lower explosion limit.
Now, in such a drying apparatus at a plurality of measuring points gas samples are withdrawn and their concentration determined by means of FIDs, an FID being associated with each withdrawal point and each FID being controlled by a program generator, also referred to as a programmer.
The programmer is provided with an alarm means which responds on occurrence of a fault within the part of the plant monitored by said means.
Such a fault can occur in the monitored measuring point but also in the FID itself.